Internal combustion engines, which are mainly used as vehicle engines, may be classified into a 4-cycle engine and a 2-cycle engine. The 4-cycle engine has a compression stroke, a suction stroke, a combustion stroke, and an exhaust stroke.
Such an internal engine uses an ignition plug in order to burn a gas mixture in a combustion stroke. That is, the ignition plug means a spark discharge device for igniting a gas mixture compressed in an internal engine.
Generally, where such an ignition plug is used in spark ignition type internal combustion engine using high-octane gasoline, the ignition timing point of the ignition plug should be determined depending on the rotating speed of the internal combustion engine, in order to obtain a combustion efficiency for an appropriate output power required in the high-performance internal combustion engine.
For example, when the rotating speed of the internal combustion engine is low, ignition is carried out at the point of time corresponding to a crankshaft angle of about −6° from a top dead center (TDC), namely, a position earlier than the TDC by an angle of about 6° As the rotating speed of the internal combustion engine increases, the ignition timing point is further earlier than the TDC. That is, when the rotating speed of the internal combustion engine increases, an advanced ignition is carried out to obtain a maximum engine output power. Although the point of time when the advanced ignition is generated depends on the rotating speed of the internal combustion engine, the advanced ignition is typically generated at an angle of about −50° from the TDC
Meanwhile, the internal combustion engine is provided with an electronic control unit (ECU) for controlling the air-fuel ratio between the amount of sucked air and the amount of injected fuel in the internal combustion engine. In detail, the ECU controls the amount of injected fuel and the ignition timing point, based on the revolutions per minute (RPM) of the engine, the amount of sucked air, and the pressure of sucked air. The ECU also has a regulation function for suppressing emission of unburned hydrocarbon (HC), carbon monoxide (CO), etc. while improving the maximum air-fuel ratio of the internal combustion engine. Thus, the ECU functions to optimize the performance of the engine.
However, the mechanism for obtaining the maximum output power of the engine cannot reduce nitrogen oxides (NOx) harmful to the human body. In particular, the problem caused by nitrogen oxides (NOx) becomes more severe in vehicles using LPG (a gas mixture of propane and butane).
In order to reduce nitrogen oxides (NOx) to an appropriate environmental pollution limit or less, an expensive three-way catalytic converter may be attached to an appropriate region of a system from which exhaust gas is discharged. The three-way catalytic converter controls emission of nitrogen oxides (NOx) to be a standard limit or less.
In this case, however, unburned hydrocarbon is accumulated due to the three-way catalytic converter. As a result, the system may be blocked or damaged.
Recently, for an improvement in engine performance, an ignition plug has been proposed which has a pre-combustion chamber structure in the form of an encapsulated structure, a tube-shaped structure, or a cover-attached structure.
However, the proposed structures incur a reduction in fuel efficiency, misfire caused by overheat at the TDP, and abnormal ignition. As a result, there is another problem such as a reduction in output power or a degradation in operation performance in the case of a high-performance engine.
Furthermore, the lower end of the pre-combustion chamber in such an ignition plug for example, an encapsulated cover, may be overheated beyond the heat exchange capability of the ignition plug namely, the heat range of the ignition plug due to high-temperature heat and vortex heat source gas present in the cylinder. Due to such overheat, detonation such as earlier ignition in a compression stroke may occur. As a result, a phenomenon that the engine is abruptly stopped may occur.